The present invention relates to a multi-cavity injection molding apparatus and method for making single or multi-layer molded products. More specifically, it relates to an apparatus and method for injection molding with a high-speed shuttling system.
Multi-cavity injection molding apparatus for making single or multi-layer molded products, such as protective containers for food, preforms for beverage bottles, and closures, are well-known. One or more types of molten material are typically injected into a cavity from a nozzle aligned with the cavity to form the molded product. Once the molten material in the cavity has cooled enough to solidify, the injection molding apparatus is usually opened to eject the molded product from the cavity. In order to properly cool and solidify, however, the molten material must remain in the cavity aligned with the nozzle for several seconds before the injection molding apparatus can be opened. As a result, the injection molding apparatus has to wait this same amount of time before the cavity can be refilled with new molten material to form a new molded product. This arrangement causes the injection molding apparatus of the prior art to have relatively high cycle or production times. While decreasing the amount of cooling time for the molded products can help reduce this relatively high cycle or production time, such a decrease in the cooling time can result in a lower quality molded product.
Some attempts have been made to overcome the disadvantages associated with the injection molding apparatus of the prior art. For example, in U.S. Pat. No. 4,472,131 to Ryder, an injection molding apparatus for preforms is disclosed that comprises alternate rows of injection and cooling cavities on a stationary plate. Ryder teaches injecting molten material into the injection cavities, and then moving the preform into a cooling cavity for post-mold cooling. In order to eject the preform from the apparatus, however, Ryder discloses the use of a complex, combined mechanical and pneumatic ejection device. While allowing a shorter overall cycle time, the pressurized air used by the complex ejection device required by Ryder may cause damage to the preforms, especially if the preforms have not fully cooled.
Another attempt to reduce the cycle time required by prior art injection molding apparatus is disclosed in U.S. Pat. No. 5,051,227 to Brun. Similar to Ryder, Brun also discloses an injection molding apparatus for preforms that comprises alternate rows of injection and cooling cavities on a stationary plate. After the injection step, Brun teaches that the mold cores are removed from the preforms while retaining the preforms using neck rings. According to Brun, a stripper plate carrying the neck rings is then moved laterally between two positions in alignment with the injection and cooling cavities. Brun then teaches inserting the molded preforms into the cooling cavities, while blowing pins are introduced inside the preform for enlarging the preforms to make contact with the walls of the cooling cavities. The injection molding apparatus disclosed by Brun, however, requires that the preforms be removed from the mold cores during the lateral movement of the preforms between the injection and cooling cavities. Besides requiring additional cooling steps (i.e., the use of blowing pins), Brun does not provide internal cooling or support for the molded preforms with the mold cores. As a result, without the mold cores, the preforms are subject to damage during their lateral movement, since they may not be totally cooled or supported.
Yet another example of an attempt to overcome the high cycle times of the prior art injection molding apparatus is disclosed in U.S. Pat. No. 5,589,130 to Takada. Takada teaches a vertical injection molding apparatus that has a rotary mold core plate with at least two positions. In the first position disclosed by Takada, preforms are injection molded and cooled while the injection molding apparatus is in the closed position. In the second position disclosed by Takada, the injection molding apparatus is opened, and the molded preforms retained on the mold cores are transferred to a cooling and ejection station through a rotary movement of the mold core plate. While a new batch of preforms are injected in the first position, Takada teaches ejecting the cooled molded preforms in the second position. The post-mold cooling of the preforms in the second position disclosed by Takada, however, is done only internally by the mold cores. Thus, the preforms are not cooled from the outside in the second position disclosed by Takada, resulting in a longer amount of time needed to properly cool the preforms. In addition, the finally cooled preforms in Takada are ejected in the second position through a two-step process: first, the preforms are pushed off of the cooling cores; and second, the two neck rings holding and cooling the preform are separated to completely release the preform. By requiring two separate movements for ejecting the preforms, Takada adds more time to the total cycle or production time of the injection molding apparatus. In addition, the ejection mechanism of Takada acts upon all the preforms at once, resulting in a diminished amount of cooling time for one or more of the preforms.
Other attempts to overcome the high cycle times and disadvantages associated with the prior art injection molding apparatus have similarly fallen short, and/or have created other disadvantages that reduce the overall efficiency and simplicity of the injection molding apparatus. Examples include U.S. Pat. No. 5,501,593, EP Patent Application No. 0 688 651 A1, and EP Patent Application No. 0 873 840 A1.
Accordingly, it would be desirable to have an apparatus and method for injection molding that overcomes the problems associated with the prior art by implementing an efficient shuttling system that reduces the overall cycle or production time for the products to be molded. In particular, it would be desirable to have a shuttling system that minimizes cycle time, while maximizing cooling time for the molded products. In addition, it would be desirable to have a shuttling system that does not use complex ejection mechanisms, such as those using pneumatic means or a multi-step process, and yet provides proper internal and external cooling and support of the molded products during operation of the injection molding apparatus. It would also be desirable to use a shuttling system that can be readily implemented into standard injection molding apparatus, as opposed to specially designed injection molding apparatus.
Moreover, there is a need for an improved, simple, and fast ejection mechanism that acts solely on the post-molding cooled products. There is also a need for an improved, simple, and fast robot device to handle and remove the post-molding cooled products. Consequently, there is also a need for an improved control system to coordinate the movements of the shuttling system, ejection mechanism, and robot device to reduce the overall cycle time and increase the efficiency of the injection molding apparatus.
The present invention provides an injection molding apparatus for molding products comprising at least one nozzle capable of injecting a molten material and a first mold part having at least one injection cavity for receiving molten material. The at least one injection cavity is aligned and in communication with the at least one nozzle. The first mold part also has at least a pair of cooling chambers flanking the at least one injection cavity. In addition, the injection molding apparatus comprises a second mold part having a laterally moveable shuttle plate with a first mold core and a second mold core. The first and second mold cores are capable of being aligned with and inserted into both the at least one injection cavity and the cooling chambers. Moreover, a first product can be formed on the first mold core in the at least one injection cavity, while a second product is simultaneously cooled in one of the cooling chambers, and the second product can be formed on the second mold core in the at least one injection cavity, while the first product is simultaneously cooled in another cooling chamber.
In addition, the present invention provides a shuttling system for an injection molding apparatus comprising a first mold part having a cavity plate with at least one injection cavity positioned between at least a pair of cooling chambers, and a second mold part having a laterally moveable shuttle plate with a first mold core and a second mold core. The first and second mold cores are capable of being aligned with and inserted into both the at least one injection cavity and the cooling chambers., The shuttling system of the present invention further comprises a first ejection mechanism for the first mold core and a second ejection mechanism for the second mold core, with the first ejection mechanism capable of being actuated independently of the second ejection mechanism.
The present invention also provides a method for injection molding of products comprising the steps of moving a first mold core into an injection cavity to form a first cavity, and injecting molten material into the first cavity to form a first product on the first mold core. In addition, the method of the present invention comprises the steps of cooling a second product on a second mold core in a first cooling chamber, while the molten material is injected into the first cavity, and moving the first product on the first mold core into a second cooling chamber. The method of the present invention further comprises the steps of ejecting the second product from the second mold core, moving the second mold core into the injection cavity to form a second cavity, and injecting molten material into the second cavity to form a third product on the second mold core. Additionally, the method of the present invention comprises the step of cooling the first product on the first mold core in the second cooling chamber, while the molten material is injected into the second cavity.